Conventionally, there is known an internal combustion engine in which an intake pipe downstream of a throttle valve and an exhaust pipe are connected with each other via an exhaust gas recirculation passage and an exhaust gas recirculation control valve, for controlling an amount of recirculated exhaust gas flowing through the exhaust gas recirculation passage, is disposed in the exhaust gas recirculation passage.
In such an engine, in order to make an air-fuel ratio accurately equal to a target air-fuel ratio, it is necessary to obtain an amount of fresh air charged in a cylinder, i.e., a cylinder-charged air amount, accurately.
Thus, there is publicly known an internal combustion engine in which a model is built while taking account of both an amount of fresh air passing through the throttle valve and then flowing into the intake pipe, i.e., a throttle valve passing-through air amount, and an amount of the recirculated exhaust gas passing through the exhaust gas recirculation control valve and flowsing into the intake pipe, i.e., an exhaust gas recirculation control valve passing-through gas amount, and the cylinder-charged air amount is calculated using this model (see Japanese Unexamined Patent Publication (Kokai) No. 2002-147279).
However, in this Publication, there is no specific description regarding how to obtain the amount of the recirculated exhaust gas passing through the exhaust gas recirculation control valve.